1. Field of the Invention
The present invention relates to an application apparatus and an image forming apparatus, and particularly relates to an application technology for applying liquid to a sheet-like medium such as a cut sheet.
2. Description of the Related Art
As a general image forming apparatus, there is an inkjet recording apparatus, which forms a desired image on a recording medium by ejecting and depositing a plurality of colors of inks onto the recording medium from a plurality of nozzles provided in an inkjet head. The recording media used in the inkjet recording apparatus are not just paper media, but also include media of a plurality of types, such as resin sheet, metal sheet, and the like, and furthermore media of various sizes and thicknesses are used.
There are some inkjet recording apparatuses that employ a method in which, in order to accomplish highly precise image formation, a recording medium before an image is rendered is supplied with aggregating treatment liquid for aggregating or insolubilizing ink and then the ink is deposited onto the recording medium. Application of this two-liquid aggregation method can realize preferred image formation without causing ink bleed or color displacement even when not only a paper medium but also a resin sheet, a metallic sheet, or any other non-(hardly-)permeable medium is used.
A roller application method with an application roller is used as a method of evenly applying the aggregating treatment liquid to the entire surface of a recording medium (a relatively wide area of the recording medium). The roller application method is capable of applying a large amount of application liquid (the aggregating treatment liquid) to the recording medium irrespectively of the properties of the application liquid, and of forming an application liquid layer with even thickness onto the recording medium.
Japanese Patent Application Publication No. 11-268444 discloses a varnishing apparatus that feeds an application cylinder with varnish, the amount of which is measured by a transfer roll, and brings the application cylinder into contact with a printing sheet held on an impression cylinder, to apply the varnish to the printing sheet.
However, when a plurality of sheets (recording media) are applied with the liquid by means of the roller application method, the application quantity on a single recording medium changes due to the return liquid that is not applied onto the recording medium from the liquid fed to the application roller.
Problems caused by the related art are described with reference to FIGS. 14A to 14D and FIG. 15. FIGS. 14A to 14D are schematic diagrams explaining a roller application method that uses an application roller 300 to apply an application liquid to a plurality of sheets (recording media) 304 held on the circumferential surface 302A of an impression cylinder 302. FIG. 15 is a diagram showing an application state in which the sheets 304 are applied with the application liquid by the roller application method.
FIG. 14A shows a state in which a first recording medium 304-1 is applied with a liquid. A certain amount of the liquid that is accumulated on an application tray 306 is measured by a measuring roller (anilox roller) 308 and fed continuously to an application roller 300. The liquid held on the surface of the application roller 300 is applied on a recording medium 304 that is moved as the cylinder 302 rotates.
Because the feeding of the liquid from the measuring roller 308 to the application roller 300 continues even at the time of non-application when the recording medium 304 is not applied with the liquid, the liquid in an amount corresponding to a plurality of times of measurement performed the measuring roller 308 is fed to the application roller 300 at the time of non-application. As shown in FIG. 14A, when applying the liquid to the first recording medium 304-1, the liquid 310A in an amount corresponding to the plurality of times of measurement is applied upon the first rotation of the application roller 300.
On the other hand, when the first recording medium 304-1 is applied with the liquid in the second and subsequent rotations of the application roller 300, the recording medium is applied with the liquid 310B in an amount corresponding to a single measurement performed by the measuring roller 308. On the first recording medium 304-1 which has been applied with the liquid as shown in FIG. 14B, an area corresponding to the first rotation of the application roller 300 from a front end part 14A has been applied with a relatively thick liquid layer, and an area corresponding to the second rotation of the application roller 300 has been applied with a relatively thin liquid layer.
FIG. 14B shows a state in which a second recording medium (indicated by a reference numeral 304-2 in FIG. 14C) reaches a processing area of the application roller 300 after the application of the liquid onto the first recording medium 304-1 (a state at the time of non-application). As shown in FIG. 14B, the application roller 300 is separated from the impression cylinder circumferential surface 302A during the non-application. On the other hand, at the time of non-application as well, the application roller 300 continues to rotate and the feeding of the liquid to the application roller 300 by the measuring roller 308 is continued.
FIGS. 14C and 14D show states in which the second recording medium 304-2 is applied with the liquid. As shown in FIG. 14C, when the second recording medium 304-2 is applied with the liquid, first, the application roller 300 that is separated from the impression cylinder circumferential surface 302A is moved to come into contact with the recording medium 304-2 as soon as the second recording medium 304-2 reaches the processing area of the application roller 300, and then an application process is started.
During the period between when the application roller 300 is separated from the impression cylinder circumferential surface 302A and when the application roller 300 rotates completely (one rotation of the application roller 300 is completed), the liquid 310B in an amount corresponding to a single measurement performed by the measuring roller 308 is applied. In other words, the first area of the second recording medium 304-2 is applied with a relatively thin liquid layer.
Once the application roller 300 rotates completely after the application roller 300 is separated from the impression cylinder circumferential surface 302A, a relatively thick liquid layer is formed by adding the liquid in an amount corresponding to a single measurement performed by the measuring roller 308, to the liquid that is fed to the application roller 300 while the application roller 300 separates from the impression cylinder circumferential surface 302A. Specifically, as shown in FIG. 14D, when applying the liquid to the second recording medium 304-2, the area corresponding to the first rotation of the application roller 300 from the front end part 14A is applied with the liquid 310B in an amount corresponding to a single measurement performed by the measuring roller 308, and, out of the areas following this area, an area corresponding to the rotation of the separated application roller 300 is applied with liquid 310C which is obtained by adding the liquid in an amount corresponding to a single measurement performed by the measuring roller 308, to the liquid (the return liquid) fed to the application roller 300 during the separation.
FIG. 15 schematically shows a state in which the first recording medium 304-1 and the second recording medium 304-2 are applied with the application liquid by means of the roller application method shown in FIGS. 14A to 14D.
As shown in FIG. 15, on the first recording medium 304-1, a relatively thick liquid layer is applied onto an area 322, the length of which from the front end 320 is same as circumferential length L of the application roller (indicated by a reference numeral 300 in FIGS. 14A to 14D) in a conveyance direction, and a relatively thin liquid layer is applied onto an area 324 positioned on the rear end side of the area 322 in medium conveyance direction.
Furthermore, on the second recording medium 304-2, a relatively thin liquid layer is applied onto an area 330, the length of which from the front end 328 is L2(=L−L1) in the conveyance direction, and an area 332 subsequent to the area 330 is applied with a relatively thick liquid layer. In addition, an area 334 subsequent to the area 332 is applied with a relatively thin liquid layer. Note that L1 is a moving distance in a direction along the circumferential surface of the application roller 300 while the application roller 300 is being separated from the impression cylinder circumferential surface 302A.
In other words, in the roller application method shown in FIGS. 14A to 14D, when the plurality of recording media 304 are applied with the liquid, the application of the liquid onto a single recording medium is uneven between the area with relatively thick liquid and the area with relatively thin liquid, due to the fact that the length of each recording medium 304 in the conveyance direction does not match the circumferential length of the application roller 300.
In order to solve such a problem using the varnishing apparatus described in Japanese Patent Application Publication No. 11-268444, the blanket corresponding to the size of a sheet to be used needs to be replaced when changing the size of the recording medium. According to this method, the time consumed in the tool replacement increases, and a plurality of application rollers need to be prepared depending on the sizes of the recording media to be used.